Photovoltaic modules consist of an outer glazing material, solar cells generally encapsulated in a clear packaging for protection, and a backsheet. The solar cells are made of materials known for use in solar collectors, including, but not limited to, silicon, cadmium indium selenide (CIS), cadmium indium gallium selenide (CIGS), quantum dots. The back sheet is exposed to the environment on the backside of the photovoltaic module. The primary function of the back sheet is to provide the low water vapor transmission, UV and oxygen barrier properties and necessary to protect the silicon wafers (photocells) from degradation induced by reaction with water, oxygen or UV radiation. Because the silicon wafers are generally encapsulated in ethylene vinyl acetate (EVA) the backsheet material should adhere well to EVA when the components are laminated together in a thermoforming process.
The backsheet of the collector can be a metal, such as steel or aluminum. However, more recently polymeric materials have been used in the back sheet. Tedlar, a polyvinyl fluoride material from DuPont (U.S. Pat. No. 6,646,196); an ionomer/nylon alloy (U.S. Pat. No. 6,660,930), and polyethylene terephthalate (PET) have all been used as the backsheet layer in photovoltaic modules, alone and in combination. PET is a polymer with excellent water vapor resistance and relatively lower cost, however it is susceptible to degradation from exposure to environmental influences, such as UV radiation, IR radiation, and ozone. In many backsheet constructions, PET is protected by the use of Tedlar (PVF) films, which are tough, photo-stable, chemically resistant and unaffected by long-term moisture exposure. They also adhere well to (EVA). However, Tedlar films are relatively expensive, and do have good resistance to water vapor. Thus the combination of Tedlar film and PET provides an excellent backsheet material. Typical constructions of photovoltaic back sheets are PVF/PET/PVF, PVF/Al/PVF and PVF/PET/Al/PVF multi-layered laminated films. However these constructions can suffer from the drawback of poor adhesion of the PVF to the PET. Adhesion is typically augmented by treatment of the polymeric surfaces with corona discharge or similar technology to increase adhesion in the PVF film. Similarly an adhesive on the PVF is employed to increase adhesion.
It has now been found that the use of polyvinylidene fluoride in backsheet compositions can provide performance, processing and cost improvements over current technology. Advantageously, adhesive layers and/or surface treatment can be eliminated for the PVDF to PET laminates. Backsheets formed from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers and polyvinylidene fluoride blends can take advantage of the properties of polyvinylidene fluoride to overcome the issues listed above with other materials.